Hell’s Half Acre is a special bit of botanical heaven in the Sierra Nevada foothills where acres of brilliant wildflowers bloom in spring.  Surrounded by pine and oak forest, Hell’s Half Acre is a distinctive open habitat sometimes called a “Mehrten meadow”.  The forest opening is formed by shallow soils underlain by a hard volcanic mudflow, or lahar. Geologists call this a Mehrten Formation. Due to the cement-like layer and gentle slopes, rainfall collects in shallow depressions before slowly draining off or evaporating.  Showy, mostly native, annual plants thrive with little competition from invasive species.

Saving a Mehrten Meadow

    In the spring of 1997 the re-zoning and impending development of the 360-acre Kenny Ranch was announced. About   50 acres of the Ranch has been known as “Hell’s Half Acre” from its use as a hobo camp, illegal dump, and, possibly, from its rocky, desert-like landscape. Kenny Ranch, on the western edge of the town of Grass Valley, is prime open land planned for commercial and residential development. In reaction to the news about the future of Kenny Ranch, California Native Plant Society members and concerned neighbors campaigned to save the 27-acre parcel south of Rough and Ready Highway from destruction.
    The property is privately owned and  the future of this Mehrten meadow is still very uncertain. Redbud Chapter, CNPS, and other friends of Hell’s Half Acre envision a botanical preserve here, accessible to wildflower lovers of all ages and abilities.

The Wildflowers

   The following is a list of selected spring-flowering plants from over 100 speciesobserved  by  botanists. The largest local populations of two rare native species are found at Hells Half Acre: Sanborn’s Onion Allium sanbornii var. sanbornii, and Pratten’s Buckwheat, Eriogonum prattenianum var. prattenianum.  Both of these plants flower in June. In addition, at least ten species of plants typical of vernal pools grow here at 2,600 feet on volcanic soils, making Hell’s Half Acre a Nevada County treasure.

Native species are shown in bold print, exotic species in normal print.
(Notes by Karen Callahan, May 12, 2007)

ANACARDIACEAE(Sumac or Cashew Family)

• Toxicodendron diversilobum  Poison  Oak

APIACEAE (Carrot Family)

• Ammi visnaga  Bishop's Weed
• Perideridia bolanderi ssp. involucrata Yampah
• Sanicula tuberosa  Tuberous  Sanicle
• Tauschia hartwegii Hartweg’s Tauschia

ASCLEPIADACEAE (Milkweed Family)

• Asclepias cordifolia Purple Milkweed

ASTERACEAE (Aster Family)

• Achyrachaena mollis  Blow Wives
• Agoseris heterophylla Annual Agoseris
• Agoseris grandiflora Large Flowered Agoseris
• Calycadenia truncata Rosin Weed
• Camomilla suaveolens  Pineapple Weed
• Cirsium occidentale var. venustum Red or Venus Thistle
• Erigeron strigosus  Prairie Fleabane
• Filago gallica Fluffweed
• Hypochaeris glabra Smooth Cat's Ear
• Madia exigua Threadstem Tarweed
• Madia rammii (type locality—Nevada City) Ramm's Madia
• Madia elegans Common Madia
• Micropus californicus Slender Cottonweed
• Psilocarphus brevissimus var. brevissimus Dwarf Woolly Marbles
• Rigiopappus leptocladus  Wireweed
• Solidago californica California Goldenrod
• Tragopogon dubius Yellow Salsify
• Tragopogon porrifolius Purple Salsify
• Uropappus lindleyi Silver Puffs 

BORAGINACEAE (Borage family)

• Cryptantha affinis  Side-grooved Cryptantha
• Pectocarya pusilla  Little Pectocarya
• Plagiobothrys greenei Greene’s Popcornflower
• Plagiobothrys stipitata v. micrantha 
• Plagiobothrys scriptus Scribe Popcornflower
• Plagiobothrys tenellus  Pacific Popcorn Flower

BRASSICACEAE (Mustard Family)

• Draba verna Whitlow Grass
• Lepidium nitidum Peppergrass
• Streptanthus tortuosus  Mountain  Jewelflower
• Thysanocarpus curvipes Fringepod

CAMPANULACEAE (Bellflower Family)

• Githopsis specularoides  Blue Cups

CAPRIFOLIACEAE (Honeysuckle Family)

• Lonicera hispidula var. vacillans Hairy Honeysuckle
• Lonicera interrupta  Chaparral Honeysuckle
• Symphoricarpos albus var. laevigatus Common Snowberry

CARYOPHYLLACEAE (Pink Family)

• Minuartia douglasii Douglas’ Sandwort
• Petrorhagia prolifera Wild Carnation
• Spergularia rubra Ruby Sand Spurry

CONVOLVULACEAE (Morning-glory Family)

• Calystegia occidentalis ssp. occidentalis Western Morning-glory

CRASSULACEAE (Stonecrop Family)

• Crassula connata  Pygmy Weed
• Parvisedum pumilum  Sierra Stonecrop

CUCURBITACEAE (Gourd Family)

• Marah watsonii Wild Cucumber, Manroot

ERICACEAE (Heath Family)

• Arctostaphylos viscida Whiteleaf Manzanita
• Arctostaphylos mewukka ssp mewukka  Indian Manzanita

FABACEAE (Pea Family)

• Cytisus scoparius Scotch Broom
• Lathyrus latifolius Perennial Sweet Pea
• Lotus purshianus Spanish Lotus
• Lupinus bicolor Miniature Lupine 
• Lupinus nanus Sky or Douglas Lupine
• Pickeringia montana  Chaparral Pea
• Trifolium ciliolatum tree clover
• Trifolium depauperatum Sack Clover, Cowbag Clover
• Trifolium dubium Little Hop Clover
• Trifolium glomeratum Maiden Clover
• Trifolium pratense Red Clover
• Trifolium repens White Clover
• Trifolium variegatum White-tipped clover
• Trifolium wildenovii Tomcat Clover (formerly Trifolium tridentatum)
• Vicia americana var. truncata  American vetch
• Vicia sativa  Spring Vetch

FAGACEAE (Oak Family)

• Quercus douglasii Blue Oak
• Quercus garryana var. breweri Shin Oak, Brewer’s white oak
• Quercus kelloggii Black Oak
• Quercus lobata  Valley Oak
• Quercus wislizenii Interior Live Oak
• Quercus chrysolepis Canyon Live Oak

GENTIANACEAE (Gentian Family)

• Centaurium venustum Canchalagua

GERANIACEAE (Geranium Family)

• Erodium cicutarium  Red-stemmed Filaree

HYDROPHYLLACEAE (Waterleaf Family)

• Eriodictyon californicum Yerba Santa

IRIDACEAE  (Iris Family)

• Iris hartwegii  Hartweg’s Iris

JUNCACEAE (Rush family)

• Juncus balticus Baltic Rush
• Juncus bufonius Toad Rush
• Juncus capitatus Leafybract Dwarf Rush
• Juncus effusus Smooth Rush
• Juncus tenuis Slender Rush
• Juncus uncialis Moss Rush

ISOETACEAE (Quillwort family)

• Isoetes orcuttii Orcutt’s Quillwort 

LAMIACEAE (Mint Family)

• Monardella lanceolata Mustang Mint
• Salvia sonomensis Creeping Sage
• Scutellaria tuberosa Skullcap
• Trichostoma oblongum Mountain bluecurls
• Trichostoma simulatum Siskiyou bluecurls

LILIACEAE (Lily Family)

• Allium amplectens Paper Onion
• Allium sanbornii Sanborn's Onion (CNPS sensitive species)
• Brodiaea elegans Harvest Brodiaea
• Brodiaea purdyi  Purdy’s Brodiaea
• Calochortus monophyllus Yellow Star Tulip
• Chlorogalum pomeridianum Common Soap Plant
• Dichelostemma capitatum Blue Dicks 
• Fritillaria micrantha Brown Bells
• Fritillaria recurva Scarlet Fritillary
• Lilium humboldtii ssp. humboldtii Humboldt Lily (CNPS sensitive species)
• Triteleia hyacinthina White Brodiaea
• Triteleia ixioides Pretty Face
• Zigadenus venenosus  Death Camas

LIMNANTHACEAE (Meadowfoam Family)

• Limnanthes alba White Meadowfoam 

MALVACEAE (Mallow Family)

• Sidalcea hartwegii Hartweg’s Sidalcea
• Sidalcea malvaeflora  Checkerbloom

ONAGRACEAE (Evening primrose family)

• Clarkia gracilis Graceful Clarkia
• Clarkia purpurea ssp. quadrivulnera Winecup Clarkia
• Clarkia rhomboidea Diamond Clarkia
• Clarkia williamsonii Williamson’s Clarkia
• Epilobium brachycarpum Panicled Willowherb
• Epilobium ciliatum Ciliate Willowherb

PINACEAE (Pine Family)

• Pinus  lambertiana Sugar Pine
• Pinus ponderosa Ponderosa Pine
• Pinus  sabiniana Grey Pine, Foothills Pine
• Pseudotsuga menziesii  Douglas Fir

PLANTAGINACEAE (Plantain Family)

• Plantago erecta California Plantain

POLEMONIACEAE (Phlox Family)

• Linanthus liniflorus  Flax-flowered Linanthus
• Navarretia divaricata Mountain Navarretia
• Navarretia intertexta Needleleaf Navarretia
• Phlox gracilis  Slender Phlox

POLYGALACEAE  (Milkwort Family)

• Polygala cornuta var. cornuta   Sierra Milkwort

POLYGONACEAE (Buckwheat family)

• Chorizanthe polygonoides Knotted Spineflower
• Eriogonum prattenianum var. prattenianum Pratten’s Buckwheat
  Type locality: Nevada City, collected by Henry Pratten in 1851. Uncommon shrub.

• Polygonum californicum  California Knotweed
• Polygonum parryi  Parry’s Knotweed
• Polygonum persicaria Lady's Thumb

PORTULACACEAE  (Purslane Family)

• Claytonia perfoliata ssp. perfoliata  miner’s lettuce

PRIMULACEAE

• Dodecatheon hendersonii Henderson’s Shooting Star

PTERIDACEAE (Brake Family)

• Pentagramma triangularis Goldback Fern

RANUNCULACEAE (Buttercup Family)

• Delphinium gracilentum Pine Forest Larkspur
• Delphinium patens Spreading Larkspur
• Thalictrium fendleri var. polycarpum Many Fruited Meadow Rue

RHAMNACEAE (Buckthorn Family)

• Ceanothus cuneatus Buckbrush
• Ceanothus integerrimus Deerbrush
• Ceanothus lemmonii Lemmon’s Ceanothus
• Rhamnus tomentella Hairy Coffeeberry (formerly a var. of R. californica)
• Rhamnus ilicifolia Hollyleaf Redberry 
• Rhamnus rubra Sierra Coffeeberry

ROSACEAE (Rose Family)

• Chamaebatia foliolosa Mountain Misery
• Heteromeles arbutifolia Toyon, California Holly
• Horkelia tridentata  Three-toothed Horkelia
• Prunus subcordata  Sierra Plum
• Rosa canina Dog Rose
• Rubus discolor Himalayan Blackberry

RUBIACEAE (Madder family)

• Galium aparine  Goosegrass
• Galium parisiense Wall Bedstraw
• Galium porrigens var. tenue  Climbing Bedstraw

SAXIFRAGACEAE (Saxifrage family)

• Lithophragma parviflorum Prairie Star
• Saxifraga californica California Saxifrage

SCROPHULARIACEAE (Figwort family)

• Antirrhinum cornutum  Spurred Snapdragon
• Castilleja lineariloba Valley Tassels
• Collinsia parviflora Maiden blue-eyed Mary
• Collinsia sparsiflora Spinster’s blue-eyed Mary
• Gratiola ebracteata Hedge Hyssop
• Mimulus angustatus  Pansy Monkeyflower
• Mimulus guttatus  Seep-spring Monkeyflower
• Mimulus layneae Layne’s Monkeyflower
• Mimulus pulsiferae Candelabra Monkeyflower
• Mimulus torreyi  Torrey’s Monkeyflower
• Penstemon  heterophyllus  Foothills Penstemon
• Triphysaria erianthus Johnny Tuck, Butter & Egg

 VIOLACEAE (Violet family)

• Viola purpurea ssp. purpurea Mountain Violet
• Viola purpurea ssp. quercetorum (formerly V. quercetorum) Mountain Violet